The present invention is generally related to control for electromechanical machines, and, more particularly, the present invention is related to sensorless control techniques for estimating rotor position in a switched reluctance machine.
In order to properly operate a switched reluctance machine, it is generally necessary to determine the rotor position in order to appropriately commutate the currents flowing in the respective phase windings of the machine. Various devices may be used to obtain a measure of rotor position, e.g., resolvers, particularly when high resolution is required. Other devices that may be used to determine rotor position include encoders or Hall sensors. However, such devices and required associated circuitry add incremental costs and may become sources of single point failure.
In order to eliminate the need for position sensors, such as resolvers, encoders, or Hall sensors, sensorless operational techniques have been developed. Many of such techniques, however, suffer from lack of consistency due to their failure to account for machine-to-machine variation when applied to a large number of machines. Further, in some cases, such techniques require time-consuming and burdensome individual calibration of the controller configured to execute such techniques in any given machine.
The present invention proposes a new technique for rotor position estimation for switched reluctance machines. The proposed technique uses the respective magnetization curves of the machine for rotor position estimation, and its inputs are measured current and estimated flux linkage. One desirable feature of the proposed technique is that it measures the magnetization data of the machine online and approximates the magnetization data in a substantially linear manner. Hence the loss of consistency from one machine to another in high volume manufacturing is not a concern. Also, it is not necessary to calibrate the controller for each machine separately.
Generally speaking, the present invention fulfills the foregoing needs by providing in one aspect thereof a method for estimating rotor position of a switched reluctance machine. The method allows for measuring magnetization curve at respective aligned and unaligned positions of the machine. The method allows for estimating flux-linkage across a respective phase of the machine. The method further allows for computing magnetization reference data between the aligned and unaligned positions. A storing step allows for storing rotor position data based on the magnetization reference data. The stored rotor position data is indicative of rotor position variation as a function of phase current. A relating step allows to relate the estimated flux linkage to the magnetization reference data to determine, for a respective phase current, correspondence of the estimated flux linkage relative to the magnetization reference data. A retrieving step allows for retrieving stored rotor position data when said correspondence is determined. The retrieved rotor position data is the estimate of rotor position of the switch reluctance machine corresponding to the respective phase current.
In another aspect thereof, the method allows for estimating multiple rotor positions by estimating an initial rotor position using the estimated flux-linkage and phase current. The initial rotor position is compensated as a function of current to obtain the final estimated position. In yet another aspect thereof, the method uses the magnetization curve at the aligned position as a reference to run the machine sensorless and measure the magnetization curve at the unaligned position. Alternatively, the method may estimate the aligned position by detecting a sign change in the derivative of the flux-linkage or when the value of such derivative is within a predefined range about zero.
The present invention further fulfills the forgoing needs by providing in another aspect thereof, a system for estimating rotor position of a switched reluctance machine. The system includes a processor for measuring magnetization curve at aligned and unaligned positions of the machine. The system includes a flux linkage estimator configured to estimate flux linkage across a respective phase of the machine. The system further includes a processor configured to compute magnetization reference data between the aligned and unaligned positions of the machine. Memory is provided to store rotor position data based on the magnetization reference data. The stored rotor position data is indicative of rotor position variation as a function of phase current. A flux-relating module is configured to relate the estimated flux linkage to said magnetization reference data to determine, for a respective phase current, correspondence of the estimated flux linkage relative to the magnetization reference data. A data retrieval unit is coupled to said memory to retrieve stored rotor position data when that correspondence is determined. The retrieved rotor position data comprises the estimate of rotor position of the switch reluctance machine corresponding to the respective phase current.
In one aspect thereof, the system allows for estimating multiple rotor positions by estimating an initial rotor position using the estimated flux-linkage and phase current. The initial rotor position is compensated as a function of current to obtain the final estimated position. In another aspect thereof, the system uses the magnetization curve at aligned position as a reference to run the machine sensorless and measure the magnetization curve at unaligned position. Alternatively, the system estimates the aligned position by detecting the change of sign of the derivative of the flux-linkage or when it becomes zero.